A method for detecting misfires in an internal combustion engine is known from German Patent No. DE 41 38 765, in which the time between two combustions, referred to as the segment duration, is detected and the roughness value of the internal combustion engine is calculated from the values determined, with the aid of physical models. If a calculated roughness value exceeds an established characteristic value, it is determined that a misfire has occurred. The fixed characteristic value is adjusted to the load and rpm ranges of the internal combustion engine. This method does not provide sufficient detection of misfires over the entire operating range of the internal combustion engine. For example, when the engine is operating with a low load at high rpm, the segment durations are very short, so that the recognition reliability can be reduced. In addition, determination of the characteristic values for different rpm and load ranges is very expensive.
It is also known that sensors can be provided in the internal combustion engine for recognizing misfires, the sensors recording, for example, the ignition voltage transformed on the primary side, or located in the combustion chamber where they measure the pressure or generate knock signals, for example. However, such sensors increase the cost of manufacturing the engine.